Evaluate plasma carcinoembryonic antigen serially in 600 patients who have gastrointestinal or other intra-abdominal malignancy, cancer of the lung or breast, and neuroblastoma by determining a baseline value on all new patients who fit into one of these categories, evaluating CEA LEVELS FOUR AND FOURTEEN DAYS AFTER SURGERY| AND ADDITIONAL TESTING DONE at 30 and 60 days and every three months thereafter. For radiation therapy patients testing at two week intervals during the therapy, and monthly intervals thereafter. Chemotherapy patients will be tested weekly for ten weeks and then monthly. Controlled plasma specimens will be assayed in each CEA test.